MC68HC05T16 Datasheet, PDF (32/128 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

4.1.3 Computer Operating Properly (COP) Reset
The MCU contains a watchdog timer that automatically times out if not reset (cleared) within a
specific amount of time by a program reset sequence.
Note: COP time-out is prevented by periodically writing a ‘0’ to bit 0 of address $FFF0.
4
If the watchdog timer is allowed to time-out, an internal reset is generated to reset the MCU.
Because the internal reset signal is used, the MCU comes out of a COP reset in the same
operating mode it was in when the COP time-out was generated.
The watchdog timer is initially disabled after a reset, it is enabled by setting the WDOG bit in the
Multi-Function Timer register (writing a ‘1’ to bit 2 of address $1C); see Section 5.2 for more
details. Once enabled, it cannot be disabled by software.
Table 4-1 shows the internal circuit actions on reset, but not necessary in order of occurrence.
Table 4-1 Reset Action on Internal Circuit
DEFAULT CONDITIONS AFTER RESET
1
Timer prescaler reset to zero state
2
Timer counter configures to $FFFC
3
All timer interrupt enable bits cleared (ICIE, OC0IE, OC1IE, and TOVFIE) to disable timer interrupt
4
All data direction registers cleared to zero (default to inputs)
5
Port E and port F configured as general purpose I/O ports
6
Configure stack pointer to $00FF
7
Force internal address bus to the address of reset vector ($FFFE)
8
Set interrupt mask bit (I bit) in condition code register to logic one
9
Clear Stop latch
10
Clear Wait latch
11
Clear all interrupt enable bits
12
COP watchdog timer reset
13
COP watchdog disabled
14
Initialize M-Bus registers
15
Initialize PWM registers
16
Initialize PAC registers
17
OSD disabled, all registers initialized to default values
Listed numbers do not represent order of occurrence.
MOTOROLA
4-2
RESETS AND INTERRUPTS
TPG
MC68HC05T16